1. Field
The present invention relates to an optical film having an antistatic layer, an antireflection film, a polarizing plate using the film, and an image display device using the film or polarizing plate on the outermost surface of the display.
2. Description of the Related Art
In the fields of optics, precision machines, building materials, home electronics and the like, lamination of an optical film having an antistatic ability is useful for the purpose of preventing, for example, dust collection or an electric circuit failure. Above all, in the field of home electronics, from the standpoint of dust protection or a countermeasure against a failure during panel fabrication, an antistatic property is required of the protective film applied to an image display device such as cathode ray tube display device (CRT), plasma display panel (PDP), electroluminescent display (ELD) and liquid crystal display device (LCD).
In addition to the antistatic property, various functions such as glare prevention, antireflection, hardcoat performance, scratch resistance and antifouling property are sometimes required of the protective film of the above-described image display device, and it is important to satisfy these functions all at the same time.
As for the method to impart an antistatic performance to an optical film used in an image display device, an antireflection film having a layer where electrically conductive inorganic metal oxide particles are dispersed in an organic binder has been conventionally known (see, JP-A-2005-196122 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2006-77113 and JP-A-2006-75698). However, the refractive index of an electrically conductive particle conventionally used in general is as high as approximately from 1.6 to 2.2 and therefore, when an inorganic metal oxide particle is used in an optical film, the refractive index of the layer containing such a particle is increased. The increase in the refractive index of the layer may allow for occurrence of unintended interference unevenness due to a difference in the refractive index from an adjacent layer or may cause a problem such as intensification of reflection tint when an antireflection layer is provided thereon.
In recent years, with the progress of clearing technique (reduction in haze) to suppress whitening due to light scattering on the surface, the optical film for display is increasingly required to cope with interference unevenness or reflection tint. Particularly, in a film where the reflectance is decreased by providing an antireflection layer, the interference unevenness becomes easily visible and therefore, it is more important to satisfy the requirement above.
On the other hand, an electrically conductive organic compound is known as an electrically conductive material replacing the inorganic oxide particle. For example, a coating film composed of a curable binder and, as an electrically conductive organic compound, a polythiophene containing a polyanion that is an electron-conducting compound, is disclosed (Patent JP-A-2004-91618 and JP-A-2006-176681).
It is also disclosed to use, as an electrically conductive organic compound, a quaternary ammonium salt group-containing compound that is an ion-conducting compound (Patent Documents JP-A-2005-54100 and JP-A-2005-316428).
However, the optical film not using an inorganic metal oxide particle with high refractive index but using the above-described electrically conductive polymer still falls short of satisfying all levels of the hardcoat property, transmittance, coating film surface shape, interference unevenness and cost.
Meanwhile, as a technique to improve the interference unevenness due to a refractive index difference from an adjacent layer, a method of suppressing the interfacial reflection by using a solvent capable of swelling or dissolving the substrate has been disclosed (JP-A-2007-249217).